ABSTRACT: Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are disorders characterized by severe gas-exchange and ventilatory abnormalities with high attendant mortality in VA patients. Sepsis due to bacterial pneumonia from virulent pathogens such as H. influenzae is the most common cause of ALI/ARDS. Cardiolipin (CL), a phospholipid present in mitochondrial and certain bacterial membranes, is minimally present in healthy lungs. However, increased levels are detected in COPD and in models of sepsis-induced lung injury. The PI and collaborators have uncovered several novel preliminary observations: i) CL is elevated in tracheal aspirates of patients with pneumonia and in murine models of pneumonitis, ii) CL potently impairs lung mechanics, and iii) an alveolar lipid pump, FIC1, binds and internalizes CL perhaps as a means to preserve alveolar homeostasis. The PI has also observed that H. influenzae infection triggers FIC1 degradation by a ubiquitin-E3 ligase-lysosomal pathway. These observations have led to the overall hypothesis in this proposal that cardiolipin is a key bioactive mediator of inflammatory lung injury and its intra-alveolar availability is tightly regulated by the exquisite bacterial-regulated phospholipid sensor, FIC1. To evaluate this hypothesis, the PI will i) determine if the pump, FIC1, is an authentic regulator of CL uptake within alveolar epithelia controlled by lipids (Aim 1), ii) determine if FIC1 is pathophysiologically regulated at the level of protein stability in response to H. influenzae infection (Aim 2), and iii) determine if CL is elevated in bronchopulmonary fluid of VA hospitalized patients with pneumonia or acute lung injury (Aim 3). The PI will execute loss-of-function and gain-of-function strategies to address causality for FIC1 control of CL, exploit use of bacterially-infected FIC1 mutant mice, and identify the molecular interactions between an SCF member E3 ubiquitin ligase and FIC1 degradation after bacterial infection. Last, the PI will perform a prospective cohort study of mechanically ventilated patients at the VA Medical Center with pneumonia to ascertain if alveolar and airway CL is a novel biomarker of illness severity. This application uniquely extends the PI's expertise in molecular physiology of lipids to whole animal and patient-oriented clinical studies. Results will provide a novel paradigm in the pathobiology of pneumonia and ALI/ARDS where new molecular targets might emerge for therapeutic intervention. PUBLIC HEALTH RELEVANCE: NARRATIVE Pneumonia is the leading infectious cause of death in the US and H. influenzae is a very important etiologic pathogen of respiratory infections in VA patients. This application proposes a new conceptual model whereby cardiolipin serves as a highly injurious bioactive molecule during pneumonitis and possibly acute lung injury. The model also implicitly predicts existence of a novel CL-binding protein(s) that may import this lipid from the alveolar or extracelular space as a salvage pathway to maintain lung homeostasis.